Bio-conversion of apple pomace into ethanol and acetic acid: Enzymatic hydrolysis and fermentation

Enzymatic hydrolysis of cellulose present in apple pomace was investigated using process variables such as enzyme activity of commercial cellulase, pectinase and β-glucosidase, temperature, pH, time, pre-treatments and end product separation. The interaction of enzyme activity, temperature, pH and time had a significant effect (P < 0.05) on release of glucose. Optimal conditions of enzymatic saccharification were: enzyme activity of cellulase, 43 units; pectinase, 183 units; β-glucosidase, 41 units/g dry matter (DM); temperature, 40 °C; pH 4.0 and time, 24 h. The sugars were fermented using Saccharomyces cerevisae yielding 19.0 g ethanol/100 g DM. Further bio-conversion using Acetobacter aceti resulted in the production of acetic acid at a concentration of 61.4 g/100 g DM. The present study demonstrates an improved process of enzymatic hydrolysis of apple pomace to yield sugars and concomitant bioconversion to produce ethanol and acetic acid.